Circuit breaker antipumping control system responsive to accumulator pressure



H. B. ASHENDEN CIRCUIT BREAKER ANTIPUMPING CONTROL SYSTEM April 22, 1958 RESPONSIVE TO ACCUMULATOR PRESSURE 2 Sheets-Sheet 1 Filed Feb. 10, 1954 QMumAXo/z m" 4/23 A fwk 1 B. ASHENDEN CIRCUIT BREAKER ANTIPUMPING CONTROL SYSTEM RESPONSIVE TO ACCUMULATOR PRESSURE Filed Feb. 10, 1954 April 22, 1958 2 Sheets-Sheet 2 CIRCUIT BREAKER ANTII'UMPING CONTROL SYSTEM RESPONSIVE T AC CUMULATOR PRESSURE Harry B. Ashenden, Cambridge, Mass., as slgnor to llis- Chalmers Manufacturing Company, Milwaukee, Wis.

Application February 10, 19s4,fsernmo. 409,303 7 Claims. c1.- 317-54 This invention relates to circuit breakers and more particularly to the closing control circuit of pneumohydraulically operated high speed circuit breakers.

A satisfactory control system fora modern power circuit breaker should perform several functions in addition to opening and closing the breaker. These functions are as follows: g

(1) Energize the closing circuit long enoughto insure complete closingeven though the closing switch initiating action is only momentarily closed.

(2) Deenergize the closing circuit to cut off the closing power just as the circuit breaker is fullyclosed.

. (3) Prevent pumping.

(4) Provide electrically trip free operation.

(5) Prevent energizing the closing circuit when the circuitbreakerisclosed. I

The term pumping is commonly used to refer to unintentional repetitive opening and closing operations of for maintaining the solenoid valve energized after the closing circuit'contacts have opened. Electromagnetic means energized when the closing switch is closedh-olds the closing circuit contacts open until the circuit breaker a breaker, while the initiating switch or closing controlswitch contact is held closed. Unless means are provided to prevent pumping, such operations can occur when a breaker is closed on a faulted line and resulting damage is probable if the fault current is high. The closing controlof .a circuit breaker should be such that it will close the circuit breaker only once for each operation of the closingcontrol switch.

In the prior art pumping was controlled or eliminated by using atwo relay control scheme which utilized a main control relay usually'designated X" and an auxiliary control relay. usually designated Y." Part of the function of the auxiliary or Y relay in the. circuit has been to provide trip free operation and to prevent pumping. It is desirable to provide a control system with fewer contacts than the prior art X, Y systems The new arrangement provides more positive sequence of action between the closing circuit deenergizing means and the antipumping means by combining these structuresin'a single device and should eliminate possible functional failure of the antipumping means caused byimperfect operation of the relay due to shock of circuit breaker operation at the time the control relayi'is attempting to seal in.

In accordance with the invention claimed, a new and improved control arrangement for closing contacts of a power circuit breaker is provided. This closing arrangement comprises a closing switch, a solenoid valve energized for admitting fluid under pressure from a source such as a pneumo-hydraulic accumulator to a motor cylinder to close the circuit breaker contacts, and a pressure operated switch responsive to pressure on one side of the motor piston for holding closing circuit contacts closed through which the solenoid valve is energized upon closing of the closing switch to initiate'closing of the circuit breaker. The pressure operated switch is responsive to a substantially simultaneous reduction of pressure on the one side of the motor piston and an increase on the other side to close the contacts of a holding circuit closes and the closing switch reopens. 1 The pressure on the other side of the piston when the circuit breaker closes rapidly actuates thepressure operated switch to open the holding circuit contacts to deenergize the solenoid and transfer accumulator pressure to the one side of the motor piston to rapidly return the piston to permit opening of the circuit breaker contacts.

1 It is therefore one objectof the present invention to provide a new and improved control'system for circuit breakers of the fluid operated .high speed type in which.

unintentional repetitive opening and closing operations of a circuit breaker are prevented.

Anotherobject of. this invention is to provide a new and'improved closing control'system for a fluid operated circuit breaker in which the circuit breaker contacts close only once for-each operation of a control switch.

' further object of this invention is to provide a new and improved circuit breaker operating mechanism in which circuit breaker control is obtained with a minimum of partsf Another object ofthis invention is to provide a fluid operated circuit breaker with a new and improved closing control system including electrical contacts interlocked with the hydrauliesystem including a ,pneumo-hydraulic accumulator to utilize the speed of fluid flow for a high speed reclosing of the circuit breaker.

Other objectsand advantages of the invention will becomeapparent from the following description when read in connection with theaccompanying drawing, in which;

. Figure 11 is a diagrammatic view of a circuit breaker,

a control circuit, and operating mechanism therefor embodying the present invention; and 7 Figure 2 is a diagrammatic view of another circuit breaker, control circuit, andoperating mechanism thereforalso embodying the present invention. l

Referring more particularly to Figure l of the draw-v ings by characters of reference, a pneumatic motor 3 of the cylinder and piston type is operatively-connected to a circuit breaker 4.

As diagrammatically shown, circuit breaker. 4 comprises a pair of stationary contact members 5 and a mov able contact-member 6. The circuit breakeris biased 'to open circuit position by means of an accelerating spring *7. 'The'rnovable contact member 6 is suitably occurrence of fault from the powerv line 15 by means or Solenoid 1 4 actuates latch fault responsive relay 1"6. 9 counterclockwise to releasebreaker rod8 to cause separation of contacts 5 and 6 of circuit breaker 4. The fault responsive relay 16'comprises .la movablev contact 17 for engaging apairof stationary 'contacts18.

In order to close circuit breaker 4, a suitable liquid under pressure such as oil is admitted to hydraulic motor 1 3. ,The motor comprises a cylinder 20, a piston '21, a ram 22 For operating the hydraulic motor the oil under pressure is'supplied to the motor from a pneumohydraulic accumulator 23. The accumulator comprises a rubber bladder filled'with nitrogen 'and confined under pressure by the oil in shell 25. -Apoppet valve 26 admits to accumulator frbm a reservoir 27 means of Patented Apr. 22, .1958

a suitable pump such as a motor driven hand pump 19.

Accumulator 23 is connected to motor 3 through suitable valve means such as a control valve 29. A solenoid 46 controls valve 29 in any suitable known manner. The solenoid preferably actuates the valve stem of valve 29 or of a high speed pilot valve 30 connecting valve 29 to accumulator 23. The solenoid valve 30. comprises a valve stem 31 and elements 32, 33 and 34 biased to the right as shown by spring 35. With solenoid valve stem 31 to the right, oil under pressure from the accumulator flows in pipe 36, through the'sole'noid valve, between elements 32, 33 of the solenoid valve and through pipe 37 to the left end of the control valve for holding control pump 28 or a valve stem 38 and associated elements 39, 40, 41 to the right as shown. In this position of valve stem 38 of the control valve oil is admitted from the accumulator through pipe 43, between elements 39 and 40 and through pipe 44 to the upper portion of the motor cylinder to supply oil under pressure to the top or one side of piston 21, thereby holding piston 21 and ram 22 in the down position for permitting opening of the circuit breaker without interference by ram 22.

To close the circuit breaker the solenoid valvevstem is actuated to the left against the action of spring 35 by energization of the coil of solenoid 46. With solenoid 46 energized the solenoid valve admits oil under pressure from the accumulator via pipe 36 between valve elements 33, 34 to enter pipe 47 which conducts the oil to the right end of the control valve for actuating control valve stem 38 to the left. Oil under accumulator pressure in pipe 43 then feeds through the control valve between elements 40 and 41 to enter pipe 48 connected to the bottom of the hydraulic motor to apply oil under pressure to the other side or bottom of piston 2.1. Return pipes 49, 50 from control valve and solenoid valve, respectively, return oil from low pressure ends of the valves to the reservoir 27. Thus with the solenoid valve energized the control valve is actuated to the left to bring accumulator pressure to the lower side of piston 21 causing it to move upward, pushing ram 22 against movable contact 6 to close the circuit breaker. Oil discharged from motor cylinder 20 escapes through pipe 44 through low pressure end of control valve 29 to reservoir 27. When solenoid 46 is deenergized, spring pulls solenoid valve piston to the right to reverse the pressure on the control valve piston to return it to normal position to the right. The actuating pressure then reverses the hydraulic motor by bringing accumulator pressure to the top side of the piston to force it back to the bottom of the cylinder.

For energizing and deenergizing solenoid 46 in correct sequence for proper closing operation of the breaker an electric control circuit is provided which is interlocked with the hydraulic system. The coil of solenoid valve 46 is connected in series with a closing switch 52 through normally closed contacts 54, 55 of a pressure operated switch 53. The pressure operated switch also includes normally open contacts 56, 57 which when closed complete a holding circuit for maintaining solenoid 46 energized after closing switch 52 may have reopened. Movable contact 56 is slidably mounted on a shaft 58 between a stop 45 and a spring 51 for movement therewith. Shaft 58 has a piston 59 at one end and piston 60 at the other end within cylinder 61 of the pressure operated switch. Movable contact 54 is slidably mounted on shaft 58 and biased to closed position with contact 55 by a spring. When shaft 58 moves upward a stop 67 on shaft 58 engages contact 54 to open contacts 54, 55, after contacts 56, 57 close. Piston 59 has a relatively larger head or pressure responsive area than piston 60. A pipe 62 hydraulically connects the upper end of the pressure operated switch adjacent piston 59 to orifice 63 in motor cylinder 20 to make piston 59 subject to the pressure in cylinder 20 above piston 21 when solenoid e 4 46 is deenergized and the piston is below orifice 63. Orifice 63 is open to the fluid on the other or lower side of piston 21 when piston 21 is actuated by a circuit closing operation.

A pipe 64 is connected to the lower end of the pressure operated switch. Pipe 64 is connected to pipe 47 to connect the lower end'of'the switch to the right end of solenoid valve 30, so that piston 60 is not subjected to pressure when the solenoid valve is deenergized. An oil or liquid discharge pipe connects the pressure operated switch at discharge orifice 65 to reservoir 27. Orifice 65 is disposed in cylinder 61 intermediate pistons 59 and 60. Pressure operated switch 53 also includes an electromagnet 66 energized when closing switch 52 is closed and deenergized when closing switch 52 is open. Closing of switch 52 completes a series circuit from source of power 68 through conductors 69, 86, coil 66, and conductors 85, 83 and back to source of power. Electromagnet66 is arranged in the pressure operated switch so that when piston 60 forces shaft 58 upward to close contacts 56, 57 of the holding circuit, the electromagnet will hold contact 54 in the upper position and hold contacts 5'4, 55 open until closing switch 52 reopens.

52 is closed. This completes a series circuit from source of power 68, through conductor 69, contacts 76, conductors 70, contacts 54, 55 of pressure operated switch, conductor 71; contacts 72, 73 of auxiliary pressure operated switch 74 which opens its contacts 72, 73 only upon failure of system pressure, conductor 82, coil of solenoid valve 46, conductor 83, and back to source 68.

Upon energization of the solenoid valve shown in Figure 1, its piston is moved to the left to admit fluid under pressure to pipe 47 to the right end of the control valve and also through pipe 47 to pipe 64 to the bottom of the pressure switch. The piston of control valve moves to the left to supply pressurefrom the accumulator to th'e bo't'tom or. piston 21 and connects the upper portion of the motor cylinder through pipe 44 to the low pressure or discharge side of the control valve to decrease the pressure on the top side of the motor piston and increase the pressure on the bottom side of the motor piston. In response to the reduction of pressure on the top side of the motor piston, the shaft 58 of the pressure operated 46, and conductor 83 to the source of power. Even though closingswitch 52 is only momentarily closed such energization pf solenoid valve 46 causes closing of the holding circuit immediately, for maintaining the solenoid valve energized to assure a complete closing operation of the circuit breaker,

With the solenoid valve maintained energized, the accumulator pressure applied to the bottom side of the motor piston forces the piston upward so that ram 22 closes the circuit breaker. When the circuit breaker contacts 5 and 6 are en'g'aged, piston 21 is above orifice 63 so that the accumulator pressure in the motor cylinder 20 below piston 21, through pipe 62 is again applied to piston59 of pressure operated switch 53. The pressure responsive area of piston 59 being larger than that of bottom side of themotor upon closing of the circuit breaker to actuate the shaft 58 downward and open holding circuit contacts 56, 57 to deenergize the solenoid valve. Upon deenergization of the solenoid valve, spring 35 moves solenoid valve piston 31 to the right to cause the control valve to return accumulator pressure to the top side of motor piston 21 for quickly returning it to the bottom of the cylinder source to'permitreopening of the circuit breaker'withoutram 22 being in the way and piston 60 of pressure operated switch 53 is again operatively connected to reservoir or atmospheric pressure.

Closing of the circuit breaker opens contacts 76, 77 of auxiliary switch 75 to maintain'the closing circuit open while the circuit breaker is closedwe Means also limiting each closing of the closingswitch to'only one closing operation of the circuit breaker is elfected by the electromagnet which is energized when the closing switch is closed. Closing circuit contacts 54 and 55 normally close before holding circuit contacts 56, 57 open. The electromagnet, however, holds the spring biased movable contact 54 open against the action of its spring when pressure forces piston'59 downward to open holding contacts 56, 57. The electromagnet thus prevents pumping or repeated closing attempts of the circuit breaker and permits only a single closing. operation of the breaker for each closing of the closing ,switch even though the circuit breaker is closed on a faulted line 15 or the latch 9 fails to hold. The electromagnet is connected across the source of power'68 through closing switch 52 and is energized if switch 52 is closed; I

The operating arrangement is electrically trip free as closure of latch opening switch 13 will cause the breaker to trip or open eventhough closing switch 52 is held normally held in a position to the right by a piston 91.

Piston 91 is movable ina cylinder 92 connected by a pipe 93 to they orifice 63 of motor cylinder 20. Piston 91 is subject to the pressure in motor cylinder 20 in the manner of piston 59 of pressure operated switch of Fig- I ure 1.

The pressure operated switch 88 includes a pair of 6 breaker contacts have closed, 'shaft89 is moved to the right causing stop 98 to open holding circuit contacts 96,

.97. to deenergize the solenoid. Only after reopening of closing switch 52 permitting contacts 94, 95 to close is closing of closing switch v52 effective to start another circuit breaker closing operation. The system illustrated in Figure 2 otherwise operates like the system illustrated in Figure l. p

Although but two embodiments of the present invention have been shown and described, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. In combination: a circuit breaker comprising a pair of relatively movable contacts, a source of fluid under pressure, a motor comprising a cylinder and a piston for causing engagement of said contacts, valve means for admitting fluid underpressure from said source to said cylinder and exhausting fluid being expelled under high velocity of said piston from said cylinder, said valve means controlling the actuation of said piston by providing fluid under pressure on one side of said piston to normally bias said piston to a position corresponding to the open circuit position of said breaker contacts and provided to reduce said pressure on said one side of said piston and provide fluid pressure on the other side of said piston to actuate said piston and said contacts to closed circuit position, a closing switch, a solenoid energized by closing of said closing switch for controlling said valve means to cause fluid to be admitted under pressure from said source through said valve means to said cylinder to close said contacts, a dual purpose pressure operated switch including first contacts, said pressure switch responsive to the reduction of fluid pressure on said one side of said piston in said cylinder for closing said first con- 7 tacts in a holding circuit for maintaining said solenoid energized after reopening of said closing switch and responsive to fluid pressure on said other side of said piston in said cylinder upon closing of said breaker for opening said first contacts to deenergize said solenoid.

2. In combination; a circuit breaker comprising a pair v of relatively movable contacts, a pneumo-hydraulic accumulator for supplying fluid under pressure, a motor comprising a cylinder and a piston for causing engagement' of said contacts, valve means connected to said I accumulator for admitting fluid under pressure from said contacts 94, 95 normally closed and connected in the closing circuit with closing switch 52, contacts 76, 77 of auxiliary switch on the coil of the solenoid valve. Another pair of contacts 96,97 normally open, are in a holding circuit for the solenoid valve. Movable contact 96 is biased toward closed position by a spring secured to shaft 89. A-stop 98 on the shaft holds contacts 96, 97 normally open, and opens these holding circuit contacts when the shaft isactuated tothe right. i A stop 99 is arranged on the shaft 89'to engage and move movable contact 94 to open the closing circuit after the holding circuit contacts close'upon movement of shaft 89 to the left by spring 90 in response to a reduction of the fluid pressure on the one side of motor piston 21 upon energization of the solenoid valve.

The pressure operated switch 88 also includes an elecaccumulator to said cylinder and exhausting fluid being expelled under high velocity of said piston from said cylinder, said valve means controlling the actuation of said piston by providing fluid under pressure on one side of said piston to normally bias said piston to a position corresponding to the open circuit position of said breaker contacts and provided to reduce said pressure on said one side of said piston and provide fluid pressure on the other side of said piston to actuate said piston and said contacts to closed circuit position, a closing switch, a solenoid energized by closing of said closing switch for controlling said valve means to cause fluid to be admitted under pressure from said accumulator through said valve means to said cylinder to close said contacts, a dual purpose pressure operated switch including first contacts, said pressure switch responsive to reduction of fluid pressure on said one side of said piston in said cylinder for closing said first contacts in a holding circuit for maintaining said solenoid energized after reopening of said closing 7 switch and responsive to fluid pressure on said other side of said piston in said cylinderupon closing of said breaker for opening said first contacts to deenergize said solenoid.

3 In combination: a'circuit breaker comprising a pair of relatively movable contacts, a source of fluid under pressure, a motor comprising a cylinder and a piston for causing engagement of said contacts, valve means for admitting fluid under pressurefrom said source to said cylinder and exhausting fluid being expelled under high velocity of said piston from said cylinder, said valve means controlling the actuation of said piston by providing fluid under pressure on one side of said piston to normally bias said piston to a position corresponding to the open circuit position of said breaker contacts and provided to reduce said pressure on said one side of said piston and provide fluid pressure on the other side of said piston to actuate said piston and said contacts to closed circuit position, a closing switch, a solenoid energized by closing of said closing switch for controlling said valve means to cause fluid to be admitted under pressure from said source through said valve means to said cylinder to close said contacts, a dual purpose pressure operated switch including first and second contacts, said pressure switch responsive to the reduction of fluid pressure on said one side of said piston in said cylinder for closing said first contacts and opening said second contacts, saidfirst contacts being in a holding circuit for maintaining said solenoid valve energized after opening of said second contacts or re opening of said closing switch and responsive to fluid pressure on said other side of said piston in said cyiindcr upon closing of said breaker for opening said first contacts to deenergize said solen'oid, said second contacts being in series with said solenoid and said closing switch, and

means limiting each said closing of said closing switch to only one closing operation of said circuit breaker, said limiting means comprising an electromagnet responsive to said closing of said-closing switch for holding said second contacts open until said closing switch has re opened to prevent energization of said solenoid through said closing switch after opening of said first contacts of said holding circuit.

4. In combination: a circuit breaker comprising a pair of relatively movable contacts, a source of fluid under pressure, a motor comprising a cylinder and a piston for causing engagement of said contacts, valve means for admitting fluid under pressure from said source to said cylinder and exhausting fluid being expelled under high velocity of said piston from said cylinder, said valve means controlling the actuation of said piston by providing fluid under pressure on one side of said piston to normally bias said piston to a position corresponding to the open circuit position of said breaker contacts and I provided to reduce said pressure on said one side of said piston and provide fluid pressure on the other side of said piston to actuate said piston and said contacts to closed circuit position, a closing switch, a solenoid energized by closing of said closing switch for controlling said 'valve means to cause fluid under pressure to be admitted from said source through said valve means to said cylinder to close said contacts, dual purpose pressure operated switch including first contacts, said prcssure switch responsive to the reduction of fluid pressure on said one side of said piston in said cylinder for closing said first contacts in a holding circuit for maintaining said solenoid energized after reopening of said closing switchand responsive to fluid pressure on said other side of said piston in said cylinder upon closing of said breaker for opening said first contacts to deenergize said solenoid, and auxiliaryswitch having contacts in series with said closing switch and said solenoid, and means opening said auxiliary switch contacts upon closing of said circuit breaker to prevent energization of said solenoid when said circuit breaker is closed.

5. In combination: a circuit breaker comprising a pair of relatively movable contacts, a pneumo-hydraulic accumulator for supplying fluid under pressure, a motor comprising a cylinder and a piston for causing engagement of said contacts, valve means for admitting fluid under pressure from said accumulator to said cylinder and exhausting fluid being expelled under high velocity of saidpiston from said cylinder, said valve means controlling the actuation of said piston by providing fluid under pressure on one side of said piston to normally 8 a bias said piston to a position corresponding to the open circuit position of said breaker contacts and provided to reduce said pressure on said one side of said piston and provide fluid pressure on the other side of said piston to actuate said piston and said contacts to closed circuit position, a closing switch, a solenoid energized by closing of said closing switch for controlling said valve means to cause fluid to be admitted under pressure from said accumulator through said valve means to said cylinder to close said contacts, a dual purpose pressure operated switch including first and second contacts, said pressure switch responsive to the reduction of fluid pressure on said one side of said piston in said cylinder for closing said first contacts and opening said second contacts, said first contacts being in a holding circuit for maintaining said solenoid energized after reopening of said closing switch, and said pressure switch being responsive to fluid pressure on said other side of said piston in said cylinder upon closing of said breaker for opening said first contacts to deenergize said solenoid, said second contacts being in series with said solenoid and said closing switch, means limiting each closing of said closing switch to only one closing operation of said circuit breaker, said limiting means comprising an electromagnet responsive to said closing of said closing switch forv holding said sec ond contacts open until said closing switch has reopened to prevent energization of said solenoid through said closing switch after opening of said holding circuit, and an auxiliary switch having contacts .in series circuit with said closing switch, said second contacts, and said solenoid, and means opening said auxiliary switch contacts upon closing of said circuit breakervto prevent energizetion of said solenoid through said closing switch when said cifiuit breaker is closed.

6. In combination: a circuit breaker comprising a pair of relatively movable contacts, a pneumo-hydraulic accumulator for supplyingfluid under pressure, a motor comprising a cylinder and a piston for causing engagement of said contacts, valve means for admitting fluid under pressure from said accumulator to said motor cylinder and exhausting fluid being expelled under high velocity of said motor piston from .said motor cylinder, said valve means controlling the actuation of said motor piston by providing fluid under pressure on one side of said motor piston to normally bias said motor piston to a position correspond-ing to the open circuit position of said breaker contacts and provided to reduce said pressure on said one side of said motor piston and provide fluid pressure on the other side of said motor piston to actuate said motor piston and said breaker contacts to closed circuit position, a closing switch, a solenoid energized by'closing of said closing switch for controlling said valve means to cause fluid to be admitted under pressure from said accumulator through said valve means to said motor cylinder to close said breaker contacts, a dual purpose pressureoperated switch comprising a first piston having a relatively large pressure responsive area, a second piston having a relatively small pressure responsive area, closing circuit contacts and holding circuit contacts a-ctuable by movement of said pistons, said first piston holding close-d said closing circuit contacts in re- 'sponse to said accumulator pressure on'said oneside of said motor piston, said valve means upon energization of said solenoid also admitting fluid under pressure to said second piston to open said closing circuit contacts after closing said holding circuit contacts for maintaining said solenoid energized, and said first piston responsive to pressure on the other side of said motor piston upon closing of said breaker contacts to open said holding circuit contacts to deenergize said solenoid.

7. In -combination: a circuit breaker comprising a pair of relatively movable contacts, a pneumo-hydrauic accumulator' for supplying fluid under pressure, a motor comprising va cylinder and a ,piston'for causing engagement of said contacts, valve means for admitting fluid under pressure from said accumulator to said motor cylinder and exhausting fluid being expelled under high velocity of said motor piston from said motor cylinder, said valve means controlling the actuation of said motor piston by providing fluid under pressure on one side of said motor piston to normally bias said motor piston to a position corresponding to the open circuit position of said breaker contacts and provided to reduce said pressure on said one side of said motor piston and provide fluid pressure on the other side of said motor piston to actuate said motor piston and said breaker contacts to closed circuit 7 position, a closing switch, a solenoid energized by closing of said closing switch for controlling said valve means to cause fluid to be admitted under pressure from said accumulator through said valve means to said motor cylinder to close said breaker contacts, a dual purpose pressure operated switch comprising a cylinder having a first piston having a relatively large pressure responsive area, a second piston having a relatively small pressure responsive area, a shaft spacing apart said first and second pistons, a fluid exhaust port in said switch cylinder intermediate said pistons, closing circuit contacts and holding circuit contacts actuable by said pistons, said first piston hold-ing closed said closing circuit contacts in response to pressure on said one side of said motor piston, said valve means upon energization of said solenoid also admitting fluid under pressure to said second piston to open said closing circuit contacts after closing said holding circuit contacts for maintaining said solenoid energized, said first piston responsive to pressure on the other side of said motor piston upon closing of said breaker to open said holding circuit contacts to deenergize said solenoid, and means limiting each closing of said closing switch to only one closing operation of said circuit breaker, said limiting means comprising an electromagnet energizedonly when said closing switch is closed for holding said closing circuit contacts open after said holding circuit contacts have opened until said closing switch has reopened.

References Cited in the file of this patent UNITED STATES PATENTS 2,308,261 Bartlett et all Jan. 12, 1943 2,346,147 Boisseau Apr. 11, 1944 2,479,315 Coggeshall Aug. 16, 1949 2,766,404 Ashenden Oct. 9, 1956 

